(1) Field of the Invention
The present invention relates to a sealed container for use in cooking which has a heat-sealed portion partially opened when there is an increase in the internal pressure during cooking of various kinds of food including frozen foods contained therein so as to prevent rupture or deformation of the container, as well as the possibility of the contents boiling over as a result of rupture of the container.
(2) Prior Art
Various types of sealed containers containing a variety of goods have been placed on the market. All of these sealed containers, however, rupture or become deformed due to increased internal pressure when heated in a microwave oven in the ordinary state, and various techniques for preventing these problems have accordingly been developed. The specification of Japanese Utility Model Publication No. 31590/1984, for example, describes a sealed container in which a lid made of paper or synthetic resin has a slit or small hole therein, is coated on the back thereof with a hot-melt adhesive, and is attached to the opening of a sealed container. In such a container, since the hot-melt adhesive is softened by the heating or the slit or the small hole is opened by the increased internal pressure, it is possible to reduce the pressure, thereby preventing the container from rupturing. In the specification of Japanese Utility Model Un-Examined Publication No. 37402/1976, it is proposed that the internal pressure be reduced by providing a portion of the lid of the container which is thinner than the remaining portion, or by providing the lid with a small hole which is covered by a thin film, these thinly formed portions being broken by any increase in the internal pressure.
All of these methods, however, suffer from the problem that several additional production processes are needed. This makes the production of the container complex and increases the production cost. In a container which employs a hot melt having a low melting point, melted hot melt may contact the food during heating. This is undesirable for reasons of sanitation. Moreover, the thinner portion or slit formed on the lid may be broken during the distribution process.
Heat-sealed containers with a heat-sealed portion having a projecting portion have also been known. Japanese Patent Un-Examined Publication No. 64970/1981 and Japanese Utility Model Un-Examined Publication No. 110266/1985, for example, disclose a heat-sealed container in which the heat-sealed portion has a portion projecting toward the exterior of the container at an acute angle for the purpose of facilitating the opening of the container. Such a container can therefore be easily opened by hand. One objective of all of these containers is to provide for improved removal of the heat-sealed portion when external force is applied. They do not therefore necessarily result in the heat-sealed portion readily peeling off as a natural result of any increase in the internal pressure of the container.